In recent years, along with rapid progresses of displays such as liquid crystals, organic ELs and electronic papers, and electronic devices such as solar cells, touch panels, there are increasing demands for reduction in thickness and weight and increase in flexibility of devices. These demands can be met by replacing a glass material with a plastic film material. From a point of view of mass productivity, a plastic film material that can be produced by a process of roll-to-roll is desired. In this process, it is necessary to use a material for which a scratch due to contact between a film and a film or between a film and a transport roller is unlikely to occur or a dimensional change due to a tension or the like during transportation is unlikely to occur, and a material having a high elastic modulus and a high strength is required. At the same time, hardness to an extent that a scratch does not occur in actual use as an application is also required.
In general, a polyimide film is known to have a high elastic modulus and a high strength as compared to a general-purpose plastic film such as a polyethylene terephthalate film, but is colored yellow or brown. This coloring is due to a high aromatic ring density and a charge transfer interaction, and is a factor that hinders the use of the polyimide film for a display material or the like that is required to be colorless and transparent. As means for colorlessizing polyimide, the use of an alicyclic monomer (Patent Document 1) and introduction of a fluorine substituent group (Non-Patent Document 1) are known. For example, Patent Document 2 discloses, as a method for obtaining a colorless polyimide, a polyimide film composed mainly of 4,4′-(4,4′-isopropylidenediphenoxy) bis (phthalic anhydride) and 2,2′-bis (trifluoromethyl)-4,4′-diaminobiphenyl.